Fluorocarboxylic acids, such as C8 fluorocarboxylic acids and their salts, are known to have excellent chemical stability based on good heat resistance, chemical resistance, and oxidation resistance, in addition to good surface activity. These fluorocarboxylic acids, as well as their ammonium salts and metal salts, are widely known as surfactants used for polymerization of fluoroolefins such as tetrafluoroethylene, surfactants for an aqueous dispersion, and water and oil repellents. It is well known that such fluorocarboxylic acids are generally prepared by hydrolyzing the corresponding fluorocarboxylic acid fluorides.
The following process can be cited as an example of a process for preparing fluorocarboxylic acids. That is, the process comprises the steps of hydrolyzing fluorocarboxylic acid fluorides in the presence of a sulfuric acid aqueous solution to form a reaction product containing fluorocarboxylic acids and hydrogen fluorides, and removing at least some of the hydrofluoric acids from the reaction product by washing the reaction product with the sulfuric acid aqueous solution (for example, see Patent Document 1). In this method, at a temperature equal to or higher than the melting point of fluorocarboxylic acids, fluorocarboxylic acids are rendered into a molten state and separated into a hydrogen fluoride-containing sulfuric acid aqueous phase and a fluorocarboxylic acid-containing organic phase based on the low solubility of the fluorocarboxylic acids to the sulfuric acid aqueous solution. As a result, a fluorocarboxylic acid phase is obtained. Distillation is carried out on the fluorocarboxylic acid phase, so that fluorocarboxilic acids can be obtained in comparatively high purity.
In addition, the above fluorocarboxylic acids can be prepared by recovering and regenerating the fluorocarboxylic acids after used in surfactants for polymerization (for example, see Patent Document 2).
Patent Document 1: JP-W 2006-500423
Patent Document 2: JP-W 2006-501300